Anisotropy reduction in coating of conductive films

ABSTRACT

Provided herein is a device for forming a conductive film. The device includes a deposition device and an air supply. The deposition device is configured to form a wet film having conductive nanostructures and a fluid carrier on a web. The web is moved in a first direction while forming the wet film. The air supply is disposed at a side of the web and configured to apply an air flow onto the wet film. The air flow is directed onto the wet film in a second direction perpendicular to the first direction to reorient a direction of some conductive nanostructures in the wet film to define reoriented conductive nanostructures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/373,712, filed on Apr. 3, 2019, which is a divisional application ofU.S. application Ser. No. 15/343,595, filed on Nov. 4, 2016, nowpatented as U.S. Pat. No. 10,307,786B2 which is a divisional applicationof U.S. application Ser. No. 13/535,112, filed on Jun. 27, 2012, nowpatented as U.S. Pat. No. 9,573,163B2, which claims the benefit under 35U.S.C. § 119(e) of U.S. Provisional Patent Application Nos. 61/504,021,filed Jul. 1, 2011, and 61/530,814, filed Sep. 2, 2011. The entirecontents of the above-referenced applications are incorporated herein byreference in their entireties.

BACKGROUND

Conductive nanostructures, owing to their submicron dimensions, arecapable of forming thin conductive films. Often the thin conductivefilms are optically transparent, also referred to as “transparentconductors.” Copending and co-owned U.S. patent application Ser. Nos.11/504,822, 11/871,767, and 11/871,721 describe transparent conductorsformed by interconnecting anisotropic conductive nanostructures such asmetal nanowires. Nanostructure-based transparent conductors areparticularly useful as transparent electrodes such as those coupled tothin film transistors in electrochromic displays, including flat paneldisplays and touch screens. In addition, nanostructure-based transparentconductors are also suitable as coatings on color filters andpolarizers, and so forth. The above co-pending applications areincorporated herein by reference in their entireties.

To prepare a conductive film or a nanostructure network layer, a liquiddispersion of the nanostructures can be deposited on a substrate,followed by a drying or curing process. The liquid dispersion is alsoreferred to as an “ink composition” or “ink formulation.” The inkcomposition typically comprises nanostructures (e.g., metal nanowires)and a liquid carrier (or dispersant). Optional agents, such as a binder,a viscosity modifier, and/or surfactants, may also be present tofacilitate dispersion of the nanostructures and/or immobilization of thenanostructures on the substrate.

A thin film of a nanostructure network layer is formed following the inkdeposition and after the dispersant is at least partially dried orevaporated. The nanostructure network layer thus comprisesnanostructures that are randomly distributed and interconnect with oneanother and with the other non-volatile components of the inkcomposition, including, for example, the binder, viscosity modifier andsurfactant.

As disclosed in co-owned U.S. patent application Ser. No. 11/504,822cited above, roll-to-roll web coating is compatible with suchsolution-based deposition (coating) processes for transparent conductorfabrication. In particular, web-coating produces substantially uniformand reproducible conductive films on flexible substrates (“web”).Suitable roll-to-roll deposition processes can include, but are notlimited to, slot die, gravure, reverse gravure, micro-gravure, reverseroll and Mayer-bar. There is a need to further enhance the uniformityand reproducibility of conductive films.

BRIEF SUMMARY

One embodiment provides a method of forming a conductive film, themethod comprising:

providing a coating solution having a plurality of conductivenanostructures and a fluid carrier;

moving a web in a machine direction;

forming a wet film by depositing the coating solution on the moving web,wherein the wet film has a first dimension extending parallel to themachine direction and a second dimension transverse to the machinedirection;

applying an air flow across the wet film along the second dimension,whereby at least some of the conductive nanostructures in the wet filmare reoriented; and

allowing the wet film to dry to provide the conductive film.

Another embodiment provides a conductive film formed according to theabove method, where, when a first sheet resistance along the firstdimension (R_(MD)) and a second sheet resistance along the seconddimension (R_(TD)) are measured at a given location on the conductivefilm, a ratio (R_(TD)/R_(MD)) of the second sheet resistance and thefirst sheet resistance defines an anisotropy of the sheet resistances,and wherein the anisotropy is less than 2, or less than 1.5, or lessthan 1.4, or less than 1.2.

Yet another embodiment provides a conductive film, wherein anisotropiesare measured at a plurality of locations across the second dimension toprovide a maximum anisotropy and a minimum anisotropy, and wherein thedifference between the maximum anisotropy and the minimum anisotropy isless than 25%, less than 20%, or less than 15%, or less than 10%, orless than 5% of the minimum anisotropy.

A further embodiment provides a method of forming a conductive film, themethod comprising:

forming a wet film having a plurality of conductive nanostructures and afluid carrier, wherein the wet film has a first dimension and a seconddimension transverse to the first dimension; and

applying an air flow across the wet film along the second dimension,whereby at least some of the conductive nanostructures in the wet filmare reoriented.

Yet another embodiment provides a conductive film comprising a pluralityof conductive nanostructures, wherein a first dimension of theconductive film is perpendicular to a second dimension of the conductivefilm and a first sheet resistance (R_(MD)) along the first dimension anda second sheet resistance (R_(TD)) along the second dimension aremeasured at a given location on the conductive film, and wherein a ratio(R_(TD)/R_(MD)) of the second sheet resistance and the first sheetresistance defines an anisotropy of the sheet resistances, wherein theanisotropy is less than 2, or less than 1.5, or less than 1.4, or lessthan 1.2.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows the basic concept of cross-web air flow to reduceanisotropy of sheet resistance.

FIG. 2 demonstrates the anisotropy reduction as a function of theposition (Sample A was fabricated using the cross-web air flow, Sample Bis a control sample fabricated without the cross-web air flow)

FIGS. 3A and 3B show micrographs of nanowires deposited withoutcross-web air flow (A) and with cross-web air flow (B).

FIG. 4 is a schematic implementation of the cross-web air flow using anair duct as a channeling device.

FIG. 5 is a side view of an air duct that provides a substantiallyuniform amount of air flow across the entire width of the wet film.

DETAILED DESCRIPTION

In roll-to-roll coating processes, the direction in which the coatedsubstrate travels is referred to herein as the machine direction (“MD”).The direction transverse (i.e., at a right angle) to the MD is referredto as the cross-web or transverse direction (“TD”). During theroll-to-roll deposition of an ink composition of nanowires, it has beenobserved that the deposited nanowires may show increased tendency toalign in the machine direction when compared to the transversedirection. Such variation in alignment may lead to a longer range ofconnectivity of nanowires in the machine direction as compared to thatin the transverse direction. This can give rise to an anisotropy intransparent conductor sheet resistance wherein such sheet resistance islower in the machine direction (R_(MD)) than it is in the transversedirection (R_(TD)).

Provided herein is a post-deposition treatment to decrease thedifference between R_(MD) and R_(TD) by applying a cross-web air flowimmediately after the deposition of the nanowires solution. It isbelieved that the anisotropy observed in nanowire alignment is caused bypreferential alignment of the nanowires due to shear in the coating beador in the slot die during the coating process.

Rather than addressing this anisotropy during the deposition itself,reduction of the nanowires' preferential alignment in MD can be achievedafter the deposition of the wet film and when the film is stillsufficiently fluid to allow for laminar flow. As shown in FIG. 1 , a wetfilm or coating (10) is formed on a moving web (20) in a machinedirection (30). Before the wet film dries or cures, an air flow (40) isapplied, from an air supply (50) (e.g., an air knife), in a directionsubstantially transverse to the machine direction (30). It was observedthat the air flow can reduce or eliminate any preferential alignment ofthe nanowires that may occur during deposition. It is believed that thelaminar flow across the wet film leads to a certain degree ofreorientation of the nanowires, especially those that have previouslyaligned along the machine direction (i.e., perpendicular to the laminarflow).

Thus, one embodiment provides a method of forming a conductive film, themethod comprising:

(a) providing a coating solution having a plurality of conductivenanostructures and a fluid carrier;

(b) moving a web in a machine direction;

(c) forming a wet film by depositing the coating solution on the movingweb, wherein the wet film has a first dimension extending parallel tothe machine direction and a second dimension transverse to the machinedirection;

(d) applying an air flow across the wet film along the second dimension,whereby at least some of the conductive nanostructures in the wet filmare reoriented; and

(e) allowing the wet film to dry to provide the conductive film.

In various embodiments, the depositing step comprises continuouslypressuring the coating solution from a reservoir onto the moving web(i.e., by a slot die method).

In further various embodiments, the air flow is continuously applied asthe wet film travels along the machine direction. Preferably, the airflow is applied immediately after the wet film is deposited, to ensurethat the wet film is fluid enough to allow the conductive nanostructuresto reorient themselves. The time interval between the deposition and airflow depends, to a certain extent, on the volatility and amount of theliquid carrier. For an aqueous-based coating solution, air flow shouldstart within 5 seconds, or within 10 seconds, or within 20 seconds orwithin 30 seconds from deposition. It is important that at the time ofthe air flow, the film has not undergone any significant drying andtherefore the nanowires could still be reoriented by external means.

The air flow can be supplied by any means known to a skilled person inthe art. Typically, the source of air flow may be, for example, an airknife located on one side of the moving web, or an air channel or ductoverhanging the moving web. Also shown in FIGS. 2-5 , the source of theair flow may be designed to provide a uniform air flow across the entirewidth of the wet film (i.e., along the second dimension). The wet filmis then allowed to fully dry.

Without the post-deposition treatment, the anisotropy of sheetresistance (defined as the ratio of TD sheet resistance to the MD sheetresistance) may be as high as 2. In various embodiments in accordancewith the present disclosure, the anisotropy of the sheet resistance canbe less than 2, or less than 1.5, or less than 1.4, or less than 1.2.

The laminar flow on the side proximal to the air supply, due to more airflow at this position, is typically stronger than the laminar flow at alateral location farther away from the air supply. Consequently, theeffect of the laminar flow on the alignment of the nanowires can also bemore pronounced, as seen in the graph in FIG. 2 . FIG. 2 shows theanisotropy of sheet resistance as a function of the locations ofmeasurement in Sample A (without cross-web air flow) and Sample B (withcross-web air flow). The anisotropy on the right side (proximal to theair supply) was reduced from 2 to 1.2. On the left side (farther awayfrom the air supply), the reduction was only from 2 to 1.4.

In the set up as shown in FIG. 2 , a standard air knife is preferablyused to generate air flow across the coated film. More specifically, ablower channeled through an approximately 15 cm×1 cm rectangular openingwas placed at the level of the coated film approximately 0.5 mm to 10 mmfrom the edge of the coated film. The air velocity was from 0.1 m/s to10 m/s and preferably around 1 m/s. The width of the coated film was 30cm. As show in the graph of FIG. 2 , the anisotropy of the coated filmwas reduced from 2 or greater to 1.5 or less to produce a silvernanowire transparent conductive with an anisotropy of no more than 1.5.

FIG. 3A and FIG. 3B illustrate the effect of laminar flow as evidencedby the microscopic alignments of the nanowires. FIG. 3A shows nanowirealignment in a conductive film without the air flow treatment. As shown,more nanowires are aligned in the machine direction (MD) that those thatare not, indicating preferential alignments due to shear. For nanowiresthat have undergone laminar flow, as shown in FIG. 3B, there is littleevidence of preferential alignment due to the reorientation of thenanowires.

Thus, a further embodiment provides a conductive film, wherein when afirst sheet resistance along the first dimension (i.e., the machinedirection) and a second sheet resistance along the second dimension(i.e., the transverse direction) are measured at a given location on theconductive film, a ratio of the second sheet resistance and the firstsheet resistance defines an anisotropy of the sheet resistances, whereinthe anisotropy is less than 2, or less than 1.5, or less than 1.4, orless than 1.2, or in the range of 1-1.5, or in the range of 1.2-1.5, orin the range of 1.4-1.5.

The sheet resistances along the MD (R_(MD)) and TD (R_(TD)) can bemeasured by first cutting out pieces of a coated film, for example,pieces that measure 5 cm×5 cm each, and measuring by a two-point probe.Typically, the two-point probe has two stripes of conductive rubber(each 2.5 cm long) that are spaced 2.5 cm apart. Other dimensions arealso suitable, as readily recognized by a skilled person in the art.

FIGS. 2-3 also show that there may be some advantage to providing across-web flow with constant air-speed over the full width of the web inorder to induce a more uniform reduction of the anisotropy at all pointsacross the width of the web.

Thus, in a further embodiment, anisotropies are measured at a pluralityof locations across the second dimension to provide a maximum anisotropyand a minimum anisotropy, and wherein the difference between the maximumanisotropy and the minimum anisotropy is less than 25% of the minimumanisotropy. In other embodiments, the difference is less than 20%, orless than 15%, or less than 10%, or less than 5% of the minimumanisotropy.

Shown in FIG. 4 is a schematic design of a duct device (100) whichchannels the cross-web air flow to help create an air flow with constantvelocity but does not touch the web. As shown, on a web (60) that ismoving in a machine direction (70), a wet film (80) is formed throughslot die deposition (90). Before the wet film (80) dries or cures, anair flow (110) is applied, from an air duct (100) in a directionsubstantially transverse to the machine direction (70). The duct shouldnot touch the web directly, to avoid damaging or disturbing the wetcoating. Some air may be lost because a hermetic seal is impossible toinstall between the duct and the web. To correct for this loss, the ductcan be modified so that the cross section of the duct is smaller at theoutlet than at the inlet.

The duct may be placed close to a roller in the web coating line orclose to a flat area between rollers. The duct may be fabricated of anysuitable, rigid material (e.g., aluminum). Preferably, the duct isapproximately 2.5 cm in width, 1 cm tall and spans the width of thecoated film. The duct can have a semi-circular cross section, squarecross section, rectangular cross section or other shaped cross section.The bottom edges of the duct are preferably placed from about 0.1 mm toabout 10 mm from the top surface of the coated film. The duct can becoupled to an air supply source at the opening of the duct near the edgeof the coated film, as shown in FIG. 4 . The source for thecross-flowing air can be a blower, air compressor or other cross-flowair source.

In order to maintain a more constant air flow across the entire width ofthe coated film when using the rigid duct, the volume of the interior ofthe duct may be gradually reduced along its length. One embodiment ofthis structure is shown in FIG. 5 , which is a side view of oneembodiment of a rigid duct 100 in accordance with the presentdisclosure. As shown, the cross-sectional area of the duct is reducedfrom the proximal air-supply end 120 of the duct to the distal end 140of the duct. The air-supply end 120 is preferably coupled to a movingair supply, the upper sloped face of the duct 160 is closed and thelower face (180) of the duct is open to the coating film (not shown),which passes beneath the duct.

In more general terms, a potential anisotropy in sheet resistance,regardless of the specific factors that give rise to the anisotropy, canbe mitigated or eliminated by a method involving air flow. Thus, afurther embodiment provides a method of forming a conductive film, themethod comprising:

(a) forming a wet film having a plurality of conductive nanostructuresand a fluid carrier, wherein the wet film has a first dimension and asecond dimension transverse to the first dimension; and

(b) applying an air flow across the wet film along the second dimension,whereby at least some of the conductive nanostructures in the wet filmare reoriented.

In various further embodiments, the method comprises the step ofallowing the wet film to dry to provide the conductive film after theair flow is applied.

In a more specific embodiment, the wet film is continuously formed on amoving substrate, the moving substrate traveling along the firstdimension. In a particularly preferred embodiment, the wet film isformed by slot die coating in a roll-to-roll process.

In further embodiments, the air flow is continuously applied as the wetfilm travels.

The conductive film thus formed is characterized with an anisotropy, asdefined herein, of less than 2. In more specific embodiments, theanisotropy is less than 1.5, or less than 1.4, or less than 1.2, or inthe range of 1-1.5, or in the range of 1.2-1.5, or in the range of1.4-1.5.

Thus, one embodiment provides A conductive film comprising a pluralityof conductive nanostructures, wherein a first dimension of theconductive film is perpendicular to a second dimension of the conductivefilm and a first sheet resistance (R_(MD)) along the first dimension anda second sheet resistance (R_(TD)) along the second dimension aremeasured at a given location on the conductive film, and wherein a ratio(R_(TD)/R_(MD)) of the second sheet resistance and the first sheetresistance defines an anisotropy of the sheet resistances, wherein theanisotropy is less than 2, or less than 1.5, or less than 1.4, or lessthan 1.2.

In various other embodiments, the anisotropies are measured at aplurality of locations across the second dimension to provide a maximumanisotropy and a minimum anisotropy, and wherein the difference betweenthe maximum anisotropy and the minimum anisotropy is less than 25%, orless than 20%, or less than 15%, or less than 10%, or less than 5% ofthe minimum anisotropy.

The various components are described in more detail below.

Conductive Nanostructures

Generally speaking, the transparent conductors described herein are thinconductive films of conductive nanostructures. In the transparentconductor, one or more electrically conductive paths are establishedthrough continuous physical contacts among the nanostructures. Aconductive network of nanostructures is formed when sufficientnanostructures are present to reach an electrical percolation threshold.The electrical percolation threshold is therefore an important valueabove which long range connectivity can be achieved.

As used herein, “conductive nanostructures” or “nanostructures”generally refer to electrically conductive nano-sized structures, atleast one dimension of which is less than 500 nm, more preferably, lessthan 250 nm, 100 nm, 50 nm or 25 nm.

The nanostructures can be of any shape or geometry. In certainembodiments, the nanostructures are isotropically shaped (i.e., aspectratio=1). Typical isotropic nanostructures include nanoparticles. Inpreferred embodiments, the nanostructures are anisotropically shaped(i.e., aspect ratio≠1). As used herein, “aspect ratio” refers to theratio between the length and the width (or diameter) of thenanostructure. The anisotropic nanostructure typically has alongitudinal axis along its length. Exemplary anisotropic nanostructuresinclude nanowires and nanotubes, as defined herein.

The nanostructures can be solid or hollow. Solid nanostructures include,for example, nanoparticles and nanowires. “Nanowires” thus refers tosolid anisotropic nanostructures. Typically, each nanowire has an aspectratio (length:diameter) of greater than 10, preferably greater than 50,and more preferably greater than 100. Typically, the nanowires are morethan 500 nm, more than 1 μm, or more than 10 μm long.

Hollow nanostructures include, for example, nanotubes. Typically, thenanotube has an aspect ratio (length:diameter) of greater than 10,preferably greater than 50, and more preferably greater than 100.Typically, the nanotubes are more than 500 nm, more than 1 μm, or morethan 10 μm in length.

The nanostructures can be formed of any electrically conductivematerial. Most typically, the conductive material is metallic. Themetallic material can be an elemental metal (e.g., transition metals) ora metal compound (e.g., metal oxide). The metallic material can also bea bimetallic material or a metal alloy, which comprises two or moretypes of metal. Suitable metals include, but are not limited to, silver,gold, copper, nickel, gold-plated silver, platinum and palladium. Theconductive material can also be non-metallic, such as carbon or graphite(an allotrope of carbon).

Conductive Film

Through a solution-based approach, a conductive film is first formed asa wet film by depositing an ink composition on a substrate, the inkcomposition comprising a plurality of nanostructures and a liquidcarrier. As the liquid carrier (a volatile component) of the wet filmfully dries, a conductive film is formed. The conductive film comprisesnanostructures that are randomly distributed and interconnect with oneanother. As the number of the nanostructures reaches the percolationthreshold, the thin film is electrically conductive. Thus, unlessspecified otherwise, as used herein, “conductive film” refers to ananostructure network layer formed of networking and percolativenanostructures combined with any of the non-volatile components of theink composition, including, for example, one or more of the following:viscosity modifier, surfactant and corrosion inhibitor.

The liquid carrier for the dispersion may be water, an alcohol, a ketoneor a combination thereof. Exemplary alcohols may include isopropanol(IPA), ethanol, diacetone alcohol (DAA) or a combination of IPA and DAA.Exemplary ketones may include methyl ethyl ketone (MEK) and methylpropyl ketone (MPK).

The surfactants serve to reduce aggregation of the nanostructures and/orthe light-scattering material. Representative examples of suitablesurfactants include fluorosurfactants such as ZONYL® surfactants,including ZONYL® FSN, ZONYL® FSO, ZONYL® FSA, ZONYL® FSH (DuPontChemicals, Wilmington, Del.), and NOVEC™ (3M, St. Paul, Minn.). Otherexemplary surfactants include non-ionic surfactants based on alkylphenolethoxylates. Preferred surfactants include, for example, octylphenolethoxylates such as TRITON™ (×100, ×114, ×45), and nonylphenolethoxylates such as TERGITOL™ (Dow Chemical Company, Midland Mich.).Further exemplary non-ionic surfactants include acetylenic-basedsurfactants such as DYNOL® (604, 607) (Air Products and Chemicals, Inc.,Allentown, Pa.) and n-dodecyl β-D-maltoside.

The viscosity modifier serves as a binder that immobilizes thenanostructures on a substrate. Examples of suitable viscosity modifiersinclude hydroxypropyl methylcellulose (HPMC), methyl cellulose, xanthangum, polyvinyl alcohol, carboxy methyl cellulose, and hydroxy ethylcellulose.

In particular embodiments, the weight ratio of the surfactant to theviscosity modifier in the coating solution is preferably in the range ofabout 80:1 to about 0.01:1; the weight ratio of the viscosity modifierto the conductive nanostructures is preferably in the range of about 5:1to about 0.000625:1; and the weight ratio of the conductivenanostructures to the surfactant is preferably in the range of about560:1 to about 5:1. The ratios of components of the coating solution maybe modified depending on the substrate and the method of applicationused. A preferred viscosity range for the coating solution is betweenabout 1 cP and 100 cP.

The electrical conductivity of the conductive film is often measured by“sheet resistance,” which is represented by Ohms/square (or “ohms/sq”).The sheet resistance is a function of at least the surface loadingdensity, the size/shapes of the nanostructures, and the intrinsicelectrical property of the nanostructure constituents. As used herein, athin film is considered conductive if it has a sheet resistance of nohigher than 10⁸ ohms/sq. Preferably, the sheet resistance is no higherthan 10⁴ ohms/sq, 3,000 ohms/sq, 1,000 ohms/sq, or 350 ohms/sq, or 100ohms/sq. Typically, the sheet resistance of a conductive network formedby metal nanostructures is in the ranges of from 10 ohms/sq to 1000ohms/sq, from 100 ohms/sq to 750 ohms/sq, from 50 ohms/sq to 200ohms/sq, from 100 ohms/sq to 500 ohms/sq, or from 100 ohms/sq to 250ohms/sq, or from 10 ohms/sq to 200 ohms/sq, from 10 ohms/sq to 50ohms/sq, or from 1 ohms/sq to 10 ohms/sq. For the opto-electricaldevices described herein, the sheet resistance is typically less than 20ohms/square, or less than 15 ohms/square, or less than 10 ohms/square.

Optically, the nanostructure-based transparent conductors have highlight transmission in the visible region (400 nm-700 nm). Typically, thetransparent conductor is considered optically clear when the lighttransmission is more than 70%, or more typically more than 85% in thevisible region. More preferably, the light transmission is more than90%, more than 93%, or more than 95%. As used herein, unless specifiedotherwise, a conductive film is optically transparent (e.g., more than70% in transmission). Thus, the terms transparent conductor, transparentconductive film, layer or coating, conductive film, layer or coating,and transparent electrode are used interchangeably.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

The invention claimed is:
 1. A conductive film, comprising: a pluralityof conductive nanostructures, wherein: at least some of the plurality ofconductive nanostructures are reoriented, the conductive film has afirst dimension and a second dimension perpendicular to the firstdimension, both the first dimension and the second dimension areperpendicular to a normal of the conductive film, the conductive filmhas an anisotropy, which is defined as a ratio (RTD/RMD) of a firstsheet resistance (RMD) and a second sheet resistance (RTD), the firstsheet resistance (RMD) is measured at a given location along the firstdimension and the second sheet resistance (RTD) is measured at the givenlocation along the second dimension, and the anisotropy is greater than1 and less than 2 according to a reorientation of the at least some ofthe plurality of conductive nanostructures.
 2. The conductive film ofclaim 1, wherein the anisotropy is greater than 1 and less than 1.2. 3.The conductive film of claim 1, wherein: the conductive film has aplurality of anisotropies, each of the plurality of anisotropies isdefined as the ratio (RTD/RMD) of the first sheet resistance (RMD) andthe second sheet resistance (RTD), for each of the plurality ofanisotropies, the first sheet resistance (RMD) is measured at a givenlocation along the first dimension and the second sheet resistance (RTD)is measured at the given location along the second dimension, theconductive film has a maximum anisotropy and a minimum anisotropy amongthe plurality of anisotropies, and a difference between the maximumanisotropy and the minimum anisotropy is less than 25% of the minimumanisotropy according to the reorientation of the at least some of theplurality of conductive nanostructures.
 4. The conductive film of claim3, wherein the difference between the maximum anisotropy and the minimumanisotropy is less than 10% of the minimum anisotropy.
 5. The conductivefilm of claim 1, wherein the plurality of conductive nanostructures havea hollow core.
 6. The conductive film of claim 1, wherein the pluralityof conductive nanostructures have a solid core.
 7. The conductive filmof claim 1, wherein the plurality of conductive nanostructures areisotropically-shaped.
 8. The conductive film of claim 1, wherein theplurality of conductive nanostructures are anisotropic ally-shaped. 9.The conductive film of claim 1, wherein the plurality of conductivenanostructures are silver nanowires.